Self-contained, renewable power sources, such as rechargeable batteries, solar cells, and the like, permit a variety of electronic products and other electronic applications to be remotely located and operated independently from large capacity power sources, e.g., the local power company. But there are limitations. Conventional batteries store only a finite charge. Typically, the smaller the battery, the smaller the stored charge. Although solar batteries can be recharged with solar energy from the sun, the power they delivered depends upon weather conditions, seasons, and latitude. Solar cells also tend to be quite large relative to the amount of power they deliver. Large size batteries and solar cells make them less attractive for smaller and/or less expensive devices/applications. It would be desirable to have a self-powered device that has a long useable life before the device requires power supply servicing or replacement. It would also be desirable to have a self-powered device that does not require large solar panels, oversized batteries, or too many batteries/solar cells.
Small, remote, self-powered devices typically have no or only rudimentary control functionality. As a result, there is no intelligent approach to controlling how and when power should be supplied or how and when a rechargeable power supply should be recharged. Nor is there an intelligent approach for controlling how power should be supplied to different power level requirements at the device that may have different levels of importance. Accordingly, it would be desirable to intelligently control how much and when power is supplied to various power level load requirements. Still further, it would be desirable for such a power supply to be responsive to different load conditions (e.g., a brief but high peak power requirement), different load priorities, and changing environmental conditions.
It is also desirable in some instances to have such devices be able to operate over a wide temperature range, wider than is normally achieved with rechargeable battery chemistries that typically do not accept much charge below freezing temperatures. It is further desirable in some instances that the power supply guarantee power availability all days of the year and over a long life without the need to change batteries. Furthermore, it is often desirable to miniaturize the power supply, but typical solar cells with sufficient energy capacity often limit the extent of miniaturization.
The present invention relates to a self-powered apparatus that includes a solar power cell, a battery, and a load. The load may include one or more load functions performed using power provided by one or both of the solar power cell and the battery. Inclusion of a battery permits the solar power cell to be sized much smaller than if the solar power cell was the only supply of power. Also, the inclusion of the small solar cell means that the battery can be much smaller than for an equivalent device powered only by a battery. A programmable controller selectively regulates power provided to one or more load functions and also selectively regulates whether one or both of the power cell and battery supplies the power. Switching circuitry, controlled by the programmable controller, selectively couples one or both of the battery and the solar cell to supply energy for powering the load. However, the switching circuitry can be controlled so that both the solar power cell and the battery supply power.
The programmable controller also determines and prioritizes load function power requirements, and based thereon, determines which load functions will be powered based the priority of the load function requirements and the amount of power that can be supplied by the solar power cell as supplemented by the battery. Preferably, the programmable controller generally provides a low quiescent, low voltage idle power when there is no load function to be performed. If there is insufficient power or insufficient stored energy for all load functions currently requiring power, then the programmable controller only powers higher priority and/or essential load functions. When neither the solar power cell nor the battery can supply enough energy to power essential load functions for the desired time period, the programmable controller gradually (rather than abruptly) degrades essential load functionality.
In another example embodiment, the solar cell and battery are coupled to charge an energy storage device, which then supplies power to the load under the control of the programmable controller. A preferred energy storage device is a super capacitor because of its tolerance of extreme temperatures. A lithium thionyl chloride battery is preferred because of its long life and its ability to function in very extreme temperatures. This example embodiment is able to operate in a temperature range of −40° to +60° centigrade. The solar power cell is mainly used to charge the super capacitor, with the battery being used as a backup for essential load functions. If the solar power cell is not supplying sufficient charge to the super capacitor, e.g., cloudy weather conditions, the battery is switched to charge the capacitor. Once the solar power cell can supply sufficient charge to the super capacitor, the battery may be switched out.
A capacitor charge detector detects the current capacitor charge and provides current charge amount to the programmable controller. The programmable controller may selectively regulate excess charge stored on the super capacitor by “dumping” it via a resistor coupled to ground, or if the battery is of the rechargeable type, to recharge the battery.
Charging the super capacitor to a relatively high level, rather than powering the load directly from the solar cell and/or battery, enables the device to provide a relatively high peak power to a high power load. One example of a high current load might be a radio transmission from a remote metering device to a central control, data gathering station.
The use of a solar power cell ensures long term, renewable, and self-contained powering of load functionality in a remote device. Supplementing the solar power cell with a battery permits considerable reduction of the solar cell size. Intelligent programmable control optimizes power supply as well as load functionality. The solar power cell, the super capacitor for solar power storage, and the supplemental battery provide a wide operational temperature range. The solar power cell and super capacitor storage provide most of the required energy with the battery supplementing any power gaps. The combination yields a power source ideal for outdoor, remote, electronically-controlled devices with very high availability, long life, wide operating temperature range, and small size.